For three decades astronomers have catalogued thousands of planets around other stars while knowing almost nothing about the air they hold. That is beginning to change.
A chemical fingerprint
Using the near-infrared spectrograph aboard the James Webb Space Telescope, a team watched the planet pass in front of its star and measured which wavelengths of light went missing. The dip at 4.3 microns is the unmistakable signature of carbon dioxide.
We are reading the chemistry of a world we will never visit, from the shadow it casts on its own sun.
The result matters because rocky planets orbiting small, active stars were expected to be stripped bare. Finding a substantial atmosphere suggests some of them hold on.
What comes next
Follow-up observations across a wider wavelength range should reveal whether water vapour and methane are present, which would sharpen estimates of surface temperature and, eventually, habitability.
